The aim of the proposed research is to gain an understanding of the molecular mechanisms behind some basic functions of biological membranes. Towards this goal we are investigating the structures of selected membrane systems, using electron microscopy and diffraction methods of analysis. The systems being studied are: (1) Membrane-bound ribosomes. Earlier, we had determined how crystalline ribosomes are oriented on, and attached to, endoplasmic reticulum membranes (Unwin, 1977; 1979). We shall now characterise their attachment further, and correlate their configuration with that of membrane-bound ribosomes actively engaged in protein synthesis. We expect soon to establish some of the structural details associated with the process in which actively synthesizing ribosomes insert nascent protein into and through the lipid bilayer. (2) Gap junctions. In initial experiments (Zampighi and Unwin, 1979), we produced two forms of isolated junction. These had different configurations for the connexon units, from which they are constructed. We shall now determine how the forms relate to each other in three dimensions. Preliminary three-dimensional comparisons suggest that the different connexon configurations could be directly relevant to the mechanism by which gap junctions regulate the passage of ions and small molecules between cells. (3) Membrane complex of Euglena. Euglena undergo striking repetitive changes in cell shape. Our preliminary investigations indicate that these changes are the result of interaction between their regular cell membrane and regular underlying cytoskeleton. We shall analyse the structure of this complex to learn of the molecular details by which the membrane proteins and cytoskeletal components interact. Our findings may lead to an understanding of some principles of membrane-cytoskeleton cooperation which apply to many other problems in cell biology.